1. Field of the Invention
The present invention relates to carboxyl-containing isobutene copolymers, obtainable
a) by cationic polymerization of a mixture of from 1 to 99 mol % of isobutene and from 99 to 1 mol % of a 2-methylalk-1-ene of 5 to 8 carbon atoms at less than 20.degree. C. in the presence of a halogen-containing Lewis acid and PA1 b) subsequent grafting of the isobutene copolymer obtainable in this manner with an .alpha.,.beta.-ethylenically unsaturated carboxylic acid or carboxylic acid derivative at above 100.degree. C. and in the presence of a free radical initiator.
2. Description of the Prior Art
The present invention furthermore relates to a process for the preparation of such carboxyl-containing isobutene copolymers and their conversion to crosslinked isobutene copolymers. The present invention also relates to the use of such isobutene copolymers as adhesive raw material and as a sealing compound.
Polyisobutenes are prepared by cationic polymerization at low temperatures and are suitable, inter alia, as raw materials for adhesives and as sealing compounds. Depending on the field of use, low molecular weight or high molecular weight polyisobutenes may be used (Ullmanns Encyklopadie der technischen Chemie, 4th edition, volume 19, pages 221-1980).
For certain applications, for example in sealing compounds, the bonding of the highly nonpolar polyisobutene chain to the generally polar substrates, which together with the polyisobutene form the sealing compound, is insufficient. Moreover, the viscoelastic behavior of the polyisobutene in sealing compounds frequently leads to deformations, some of which go substantially beyond the tolerable extent.
In the case of polyolefins, the bonding to polar substrates is generally achieved by grafting them subsequently with carboxyl-containing monomers. In the case of polyisobutene, however, this is not possible since the polyisobutene is not sufficiently reactive for such a reaction with carboxyl-containing monomers. All that is known is that copolymeres of isobutene with 2-methylalk-1-enes can be prepared by copolymerization by means of Ziegler catalysts (DE-A 20 14 394). However, the resulting isobutene copolymers are obtained as low molecular weight, viscous oils which, owing to their poor stability, cannot be used for many applications, for example as sealing compounds.